Kinetic switches are used in various applications such as kinetic ordnance, flight recorders, missiles, guided and unguided rockets, aircraft applications and other critical applications. Kinetic switches may be hermetically sealed with inert gas for high reliability, aggressive environmental applications and they may be available in numerous sizes and packages. Kinetic switches may be un-damped, air damped or fluid damped. They may be normally open or normally closed. Kinetic switches are available as acceleration/Inertia/impact switches for applications involving acceleration, spin, impact, recoil, directional sensing vibration and g-time products available Kinetic switch designs may be tailored to specific electronic and environmental requirements. These switches are designed to respond to acceleration/deceleration in excess of a predetermined value.
Kinetic switches may be used to generate a wake-up signal to a dormant circuit in response to the beginning of an impact event, thereby activating the circuit. In its simplest embodiment, the kinetic switch may be a simple on/off switch that switches from one position, for example off, to a second position, on in response to an acceleration or deceleration event such as an impact event. An impact event may be an object striking the ground from the air, the impact causing the kinetic switch to activate a circuit. A kinetic switch may be used to trigger the inflation of an airbag in a vehicle in the event of an impact event exceeding the threshold limits of the switch.
U.S. Pat. No. 8,154,175 describes one such kinetic switch which comprises a snap mechanism provided between an input element and an output element to provide a bistable switch having two discrete positions. A first position P1 is indicative of the input state being below a given threshold, or “off” position, and a second position P2, which is indicative of the input state being at or above the threshold, or “on” position. The snap mechanism maintains a positive reacting force throughout the operating stroke of the output element. A disc in the snap mechanism deflects as the input increases until a maximum threshold force is applied to the disc at which point the disc “snaps” over. A stem provides the input element (receiving a force F) and the output element. A structure supports a snap element connected to a stem. The snap element, which may be a flexible disc, has a concave configuration with the stem in the first position P1. Upon the force F reaching a threshold force, the snap element is deflected to a convex configuration that moves the stem to the second position P2 or on position. Stops limit the travel of the stem.
Regardless of the design of the kinetic switch, it must operate reliably for its intended function, particularly for some of the critical applications described above. To assure that these kinetic switches properly operate, they are tested to assure that they switch from a first position to a second position when the predetermined set point is reached. The predetermined set point may vary from one design to the next, but the switch must reliably function when the predetermined set point is reached.
Kinetic switches are tested by placing them on a centrifuge and rotating them at high speeds. One or more kinetic switches may be tested simultaneously by mounting the switches to the centrifuge. As the centrifuges are accelerated up to speed, the switches are monitored to determine if they switch from a first position to a second position as the centrifuge reaches the predetermined speed. Each switch is connected to a test circuit that determines whether the switches in fact switch from a first position to a second position as the predetermined speed is reached, generating a signal or signals. The signal or signals are transmitted to a computer monitoring the testing via a slip ring or slip rings, which enable the transfer of signals across a rotating surface. The computer may be used to store the data indicative of the force at which each switch is activated.
One of the problems currently faced is that as the kinetic switch requirements have become more stringent, some of the forces reaching 80,000 Gs with centrifuge speeds reaching in excess of 26,000 rpm, slip ring wear also is accelerated. The slip rings are utilized to transmit data from test circuits evaluating the performance of each of the rapidly rotating kinetic switches as the rotational speed increases. Further reduction in slip ring life will result as kinetic switches requiring even higher G-forces are developed. Furthermore, chatter resulting from slip ring wear results in transmission of erroneous test data, which may lead to kinetic switches being rejected when in fact they should be accepted. Transmission of test data using wireless monitors is also not a viable solution since these wireless monitors require on-board transmitters requiring on-board batteries to transmit the test results. Of course, the batteries include chemical components which will not survive the high speeds of centrifugation for extended periods of time, experiencing premature failure and frequent replacement as well as messy and inconvenient clean-up.
What is needed is a device that can monitor the operation of kinetic switches during testing and transmit the measured test data to a recording device so that each of the tested kinetic switches and be tested to determine acceptable operation at a predetermined speed. The device must be able to both determine switch operation and transmit data indicating whether the switch operation occurs at the predetermined speed without the use of a self-contained power supply, while also eliminating the use of slip rings as a communication device.